Footnotes

• Contributors MV designed the study, analysed the data and wrote the manuscript. EC helped with study design, analysis and interpretation of the results. SP was responsible for data preprocessing, quality checking and analysis. EW was responsible for data collection and manuscript preparation. AB helped in the design of study, interpretation of results and preparation of the manuscript.

• Competing interests None declared.

• Ethics approval Individual hospital research ethics committees.

• Provenance and peer review Not commissioned; externally peer reviewed.